Long-term treatment of rats with haloperidol produced an increased sensitivity to the locomotor and stereotypic effects of apomorphine. This behavioral dopaminergic supersensitivity was also accompanied by increased (3H) spiroperidol binding in the striatum. However, rats treated concurrently with lithium and haloperidol failed to develop both behavioral sensitivity to apomorphine and increased striatal dopamine receptor binding. While chronic lithium had no effect on dopamine binding, it appeared to increase alpha-adrenergic binding and decrease beta-adrenergic binding. It is suggested that the ability of lithium to prevent recurrent manic-depressive episodes may be related, in part, to these effects on the catecholamine receptors.